This invention is generally in the field of methods of fabricating miniaturized reservoir devices for the controlled release or exposure of reservoir contents, such as drug formulations and/or sensors.
U.S. Pat. No. 5,797,898, U.S. Pat. No. 6,551,838, and U.S. Pat. No. 6,491,666, all to Santini, et al., describe microfabricated devices that have a plurality, typically hundreds to thousands, of tiny reservoirs. In some embodiments, these reservoirs are provided with a reservoir cap over the contents (such as a drug formulation) of the reservoir, so that the contents are released from the device by the controllable disintegration of the reservoir caps. For example, the reservoir cap can be a metal film and an electric potential can be applied to cause the metal film to oxidize and disintegrate. In this embodiment, the microchip device is connected to an external circuit through wire bond pads on the microchip (i.e., on the substrate), and an electrical connection between the reservoir caps and the bond pads is provided by conductive traces fabricated on the chip. The reservoir caps, traces, and bond pads can be fabricated, for example, using a single patterned layer of gold.
U.S. patent application Publication No. 2004/0121486 A1 to Uhland, et al., also describes devices having an array of micro-reservoirs each covered by a reservoir cap. The publication further describes a innovative means for disintegrating the reservoir cap to expose/release the reservoir contents: An electrical current is selectively passed through each reservoir cap, via an input lead and an output lead, in an amount effective to heat the reservoir cap to cause the reservoir cap to rupture, thus opening the reservoir. One embodiment includes reservoir caps, traces, and bond pads fabricated from a conductive material. In one embodiment, the reservoir caps and traces are fabricated from different materials and are electrically connected. It would be desirable to provide devices and fabrication methods in which the surface of the exterior or interior of the device or the substrate can be coated or altered to protect the device from the environment or to obtain a favorable surface chemistry for drug storage. It would be further desirable to provide methods for fabricating multi-reservoir devices wherein the circuitry is fabricated in a robust manner and good physical and electrical contact is maintained between features of the device that are meant to be electrically connected.
U.S. Pat. No. 6,123,861 to Santini, et al., describes forming reservoirs in a substrate by etching a single crystal silicon wafer using aqueous potassium hydroxide. Because the pyramidal reservoirs formed by this process are defined by silicon crystalline planes, the area density of reservoirs on the wafer is inversely coupled to the volume of each reservoir.
It would be advantageous to have micro-reservoir devices that have a high area density in order to pack more reservoir contents into as small a total device volume as possible, particularly for applications where the device is to be implanted into a patient (such as for controlled drug delivery or biosensing). It therefore would be desirable to develop improved devices and new methods of making them in which the reservoir volume in these devices can be increased without adversely affecting the area density of reservoirs on/in a substrate.